A friction clutch includes clutch housing having a friction plate, a clutch boss having a clutch plate, a pressure plate, a sub clutch, and a power-assist mechanism. The power-assist mechanism receives torque from the pressure plate when the clutch is disengaged and converts the torque into a force for moving the pressure plate in a direction which separates the pressure plate from a plate group. A cam surface, which supports and guides one or more roller weights, is formed on the pressure plate. The one or more roller weights move outward in a radial direction by a movement amount according to the magnitude of centrifugal force and press the pressure plate toward the plate group with force according to the movement amount.